The present invention relates to spring assemblies and, in particular, to spring assemblies adapted for use in automatic transmissions for vehicles.
Automatic transmissions for vehicles often include a plurality of spring assemblies that are adapted to apply, typically via a die-cast piston member, biasing force against clutch plate assemblies that control the engagement of the various gears in the transmission. These spring assemblies generally comprise an annular plate having a multiplicity of circumferentially spaced, parallel-oriented compression springs mounted thereto. Alternatively, the spring assembly may include a second annular plate secured to the opposite free ends of the compression springs as well. Spring assemblies of the above-described type are disclosed in U.S. Pat. No. 3,782,708.
With the advent of automatic transmissions having four, five, and even six forward gears, coupled with the need to package these transmissions in smaller overall volumes, there is a desire among automobile manufacturers to reduce the axial length of the spring assemblies while at the same time increasing the axial force of the spring assemblies without increasing the spring rate. Keeping the spring rate of the assemblies as low as possible is desirable because it helps to achieve smooth shifts.
To achieve the goals of increased force while maintaining the same spring rate dictates the use of taller compression springs. However, the use of taller compression springs also serves to correspondingly increase the axial length of the resulting spring assembly. Moreover, since the spring assemblies are typically compressed and released during assembly of an automatic transmission, the increased excursion of the spring assembly can result in damage to the seals in the transmission.
Accordingly, it is the primary object of the present invention to provide an improved spring assembly that is shorter in axial length, provides greater axial force, and yet maintains the same spring rate of conventional spring assemblies. In addition, it is also an object of the present invention to provide a spring assembly that satisfies these criteria in a reliable and cost-effective manner.
In general, the present invention accomplishes these objectives by providing taller compression springs that are precompressed between two annular plates that are interconnected at circumferentially spaced points around their peripheries. In this manner, the axial length of the overall spring assembly is controlled despite the use of taller compression springs. Moreover, the interconnection means between the two annular plates is configured so as not to restrict the compressibility of the spring assembly and thereby enable the axial length of the entire spring assembly to constrict a the springs are compressed. In other words, the axial length of the entire spring assembly according to the present invention is compressible to the same extent as a conventional spring assembly without the interconnection means. However, unlike a conventional spring assembly, the interconnection means in the present invention prevent the springs from reaching their complete free-state length and thereby controls the packaging size of the spring assembly. In the preferred embodiment of the present invention, the interconnection means is designed to limit the axial length of the spring assembly to a height slightly greater than the maximum excursion height of the spring assembly during normal operation of the transmission so that the interconnection means remains unloaded during normal operation, thereby improving reliability.
In addition, the annular plates in the preferred embodiment are formed with specially configured upstanding tabs for mounting the compression springs to the plates. In particular, the tabs are formed to a predetermined height and are oriented so that the opposed tabs on the two annular plates supporting the respective ends of each compression spring will abut one another as the springs are about to become fully compressed, thereby preventing possible overstressing or distortion of a spring, or distortion of the interconnection means.
Further, the interconnection means which are integrally formed on the annular plates are preferably designed so that the two annular plates are identical in configuration and can therefore be manufactured from the same tooling to save costs.
Additional objects and advantages of the present invention will become apparent from a reading of the following detailed description of the preferred embodiment which makes reference to the drawings of which: